The present invention relates to etching a silicon-containing material on a substrate.
In the manufacturing of electronic components, such as integrated circuits and flat panel displays, silicon-containing layers, such as silicon dioxide, silicon nitride, polysilicon, metal silicide, and monocrystalline silicon layers, are formed on a substrate. These materials may be etched, for example, to form gates, vies, contact holes, trenches, and/or interconnect lines. In the etching process, a patterned mask of silicon dioxide, silicon nitride or etch resistant polymer is formed on the substrate by conventional lithographic methods. The substrate is placed in an etching chamber and portions of the underlying silicon-containing layer which are exposed through the mask are etched, for example, by an energized gas such as a plasma or a microwave activated gas.
In the etching process, a film of etchant residue often forms on surfaces around the substrate, for example on the walls, components and other internal surfaces of the chamber. It is difficult to clean the etchant residue especially when the composition of the etchant residue varies across the chamber. The etchant residue composition depends upon the composition of the process gas, the material being etched, and the composition of the etch resistant material on the substrate. For example, when tungsten silicide, polysilicon or other silicon-containing layers are etched, vaporized or sputtered silicon-containing species form a large component of the etchant residue. In addition, the etch resistant material may also be partially vaporized to form gaseous hydrocarbon or oxygen species that become part of the etchant residue. The chemical composition of the etchant residue may also vary considerably also depending upon the local gas environment, the location of gas inlet and exhaust ports, and the spatial geometry of the chamber. The etchant residue is undesirable because it can flake off during processing and contaminate or otherwise alter the characteristics of the surfaces on which it deposits.
In a conventional process, the etch ant residue is periodically cleaned off the surfaces in the chamber. For example, in one method, after processing a batch of substrates, a dry-cleaning process is used to clean the chamber surfaces with an energized cleaning gas. However, when the energized cleaning gas is not sufficiently reactive to the etchant residue, slow and inefficient cleaning rates are obtained; and when the energized cleaning gas is too chemically aggressive it can erode the chamber walls and components. It is also difficult to control the composition and energy level of the cleaning gas to achieve the conflicting goals of high rates of removal of the etchant residue, uniform cleaning and of chamber surfaces and reduced erosion of chamber surfaces.
In another method, the cleaning gas is added to the etchant gas, and the resultant gas composition is energized to both etch the substrate and clean the surfaces in the chamber. However, it is often difficult to etch compositionally different portions of a substrate at similar etch rates using the combined gas. For example, when etching p-doped and n-doped regions in the fabrication of p-channel and n-channel CMOS transistors in symmetrical matched pairs, it is difficult to etch both doped regions at the same etch rates with the combined energized gas. Variations in their etch rates can cause the two regions to be etched to different depths.
Thus it is desirable to have an etching process that may be used to clean-off etchant residue formed on the internal surfaces of the chamber without excessive erosion of the chamber surfaces. It is also desirable for the etching process to etch compositionally different regions on the substrate at similar etch rates. It is further desirable to etch material on the substrate with a high etching selectivity to a mask or underlayer.
The present invention satisfies these needs. One aspect of the present invention comprises a method of etching a silicon-containing material in a substrate, the method comprising placing the substrate in a process chamber and providing in the process chamber an energized gas comprising fluorine-containing gas, chlorine-containing gas and sidewall-passivation gas.
Another aspect is a method of etching a substrate in a process chamber while simultaneously cleaning surfaces in the process chamber, the method comprising placing the substrate in the process chamber, the substrate comprising a silicon-containing material having a plurality of dopant concentrations or dopant types, and providing in the process chamber, an energized process gas comprising fluorine-containing gas, chlorine-containing gas and sidewall-passivation gas, whereby the plurality of dopant concentrations or dopant types in the silicon-containing material, are etched at substantially similar rates.
Yet another aspect is a process chamber comprising a substrate support, a gas source for providing process gas comprising fluorine-containing gas, chlorine-containing gas, and sidewall-passivation gas, a gas energizer, and a gas exhaust, whereby a substrate received on the support may be processed by process gas provided by the gas source, energized by the gas energizer, and exhausted by the gas exhaust.